Quality of supply is an important factor for electrical energy consumers. High voltage, high energy transient power spikes delivered along or through power supply systems can cause significant damage to electrical loads. In particular these forms of transient surges can cause significant damage to sensitive semiconductor components commonly found in domestic, industrial and commercial electronic systems.
These transient surges are characterised by high energy and high voltage but have a very short duration. A number of techniques and components have been developed to mitigate the effects of these surges, and preferably to absorb or deflect the energy they contain prior to it reaching an electrical load. Lightning strikes and inductive power dumps are the most common source of electrical transients, the occurrence of which cannot be predicted and which can deliver transient surges capable of effectively destroying a wide range of electrical loads.
In addition to surge protection switching gear deployed with a high voltage power transmission networks a number of surge protection devices have been developed for use in proximity to electrical loads or to be combined with the electrical loads itself. These localised surge protectors can—for example—be found in power supply the systems of an electrical load or in power boards or multi plug products advertised to consumers as providing some form of surge protection. These localized forms of surge protector generally incorporate some form of non-linear componentry with filters which act to provide a path to ground for electrical transients above a specific break down voltage. Examples of these devices can include gas discharge tubes, metal oxide varistors, or semiconductor devices such as breakdown diodes or thyristors which are all commonly known as transient voltage suppressor (TVS) components.
These existing types of non-linear surge protection devices can however experience gradual degradation in their performance over time. With exposure to multiple surges the break down or triggering voltage of some of these components can be lowered by each successive surge, ultimately leading to the surge protector effectively preforming as a short circuit to ground and preventing any power being supplied to a load, or acting as an ineffective unit without any protection being provided.
Another characteristic of these types of non-linear TVS components is the response time that they take prior to channelling a transient away from an electrical load. Due to the short duration and high energy characteristic of such transients it is preferable that these surge protection components act as rapidly as possible to prevent as much of the transient surge reaching a load as possible.
In practice a combination of several different types of TVS components may be employed with each component selected based on its rated response and performance characteristics.
Storage capacitors have been considered for use in these surge protection applications but have been found to be unsuitable. Although standard capacitors are able to receive charging voltages of hundreds of volts their capacitance and associated time constants mean that they will receive more than a full charge generally within the period of the transient. Although standard capacitors are readily available and inexpensive components they are unable to cope with the relatively high energy content of transients and will quickly become over charged and damaged.
A relatively new class or form of large capacitor known as a supercapacitor, electric double layer (“EDL”) capacitor, or ultra-capacitor also exists. These devices can exhibit significantly higher capacitances than commonly found versions of standard capacitors such as electrolytic, ceramic, or tantalum capacitors. These EDL capacitors can also have associated time constants or charging times which are significantly longer than such standard capacitors.
However, current commercial families of EDL capacitors are unable to receive high continuous charging voltages and are usually only rated to receive charging voltages of less than approximately 5 volts (DC). Due to these low continuous DC voltage ratings EDL capacitors are generally not considered in high energy surge protection applications.
It would therefore be of advantage to have a further class of TVS type components available to supplement or potential replace existing forms of TVS components. In particular it would be of advantage to have an improved power surge protection apparatus which could improve on the performance of prior art systems or at least allow the implementation of a protection apparatus with an improved response time and/or reliability. Any improvements which could be made in the field of transient voltage suppression which address any of the above issues or at least provide an alternative choice to the prior art would also be of advantage.